Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$124.67	10.209%	$137.3976	$137.40	$137.40	$137.40
Purchase #2	$40.98	4.602%	$42.8659	$42.87	$42.85	$42.90
Purchase #3	$213.83	5.271%	$225.101	$225.10	$225.10	$225.10
Purchase #4	$61.43	9.847%	$67.479	$67.48	$67.50	$67.50
Purchase #5	$174.99	9.646%	$191.8695	$191.87	$191.85	$191.90
Purchase #6	$216.85	10.269%	$239.1183	$239.12	$239.10	$239.10
Purchase #7	$113.61	11.819%	$127.0376	$127.04	$127.05	$127.00
7 purchase totals =	$946.36		$1,030.8689	$1,030.88	$1,030.85	$1,030.90